A constant-current power supply is capable of maintaining a preset current through a variable load resistance. A conventional constant-current power supply circuit is described in Japanese Laying Open S63-265315. The reference discloses plural constant-current power supply circuits connected to a common power supply line. Each constant-current power supply circuit is provided with P-channel field effect transistors (hereafter referred to as PMOS) and N-channel effect transistors (hereafter referred to as NMOS). Sources of PMOS and NMOS are mutually connected, while the drain of the NMOS being connected to the power supply line which supplies the power voltage. It is constructed to output constant current (constant current) from the drain of the PMOS.
Each NMOS gate is supplied with common bias power generated by a bias circuit based on the power voltage, and each of the PMOS gates is supplied with bias voltage generated by the bias circuit based on the power voltage, independently from each PMOS.
As stated in the above reference, the NMOS, installed between the PMOS and the power supply line, corrects any power voltage variation generated by the power supply line resistance in each constant-current power supply circuit. Therefore, variation of the constant-current output supplied from each constant-current power supply circuit is eliminated.
According the above-described conventional constant-current power supply circuit, however, the bias voltage supplied to the NMOS and PMOS varies due to temperature variations in the power voltage source. Therefore, the constant current output supplied from the PMOS will also vary in response to the temperature.